<Page>

                                                                    EXHIBIT 32.1

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002


In connection with the Quarterly Report of United Stationers Inc. (the
"Company") on Form 10-Q for the quarterly period ended June 30, 2004, as filed
with the Securities and Exchange Commission on the date hereof (the "Report"),
Richard W. Gochnauer, President and Chief Executive Officer of the Company, and
Kathleen S. Dvorak, Senior Vice President and Chief Financial Officer of the
Company, each hereby certify, pursuant to 18 U.S.C. ss. 1350, as adopted
pursuant to ss. 906 of the Sarbanes-Oxley Act of 2002, that:


     (1)  The Report fully complies with the requirements of Section 13(a) or
          15(d) of the Securities Exchange Act of 1934; and

     (2)  The information contained in the Report fairly presents, in all
          material respects, the financial condition and results of operations
          of the Company.


A signed original of this written statement required by Section 906 has been
provided to the Company and will be retained by the Company and furnished to the
Securities and Exchange Commission or its staff upon request.


/s/ Richard W. Gochnauer
- ------------------------------------------------------
Richard W. Gochnauer
President and Chief Executive Officer
August 6, 2004


/s/ Kathleen S. Dvorak
- ------------------------------------------------------
Kathleen S. Dvorak
Senior Vice President and Chief Financial Officer
August 6, 2004